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Microdosimetric study on influence of low energy photons on relative biological effectiveness under therapeutic conditions using 6 MV linac
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10.1118/1.3613152
/content/aapm/journal/medphys/38/8/10.1118/1.3613152
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/8/10.1118/1.3613152
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

The geometries of three kinds of the TEPC measurements: (a) the change of the field size and the change of the position perpendicular to the central beam axis (depth = 10 cm, and a source to surface distance = 90 cm) and (b) the change of the depth (a source to surface distance = 100 cm).

Image of FIG. 2.
FIG. 2.

The symbols represent the experimental RBE for cell killing of the HSG tumor cells for 200 kV x-rays (open circle), 60Co γ-rays (open triangle), and 6 MV x-rays (open square), and the solid line represents the calculated RBEMK using Eq. (6), which were reported in the previous paper (Ref. 4). 200 kV x-ray was defined as the reference radiation.

Image of FIG. 3.
FIG. 3.

(a) Comparison between the measured and the calculated depth-dose curve for a 10 × 10 cm2 field with 6 MV x-rays. The depth-dose curve was measured with an ionization chamber (CC13, Scanditronix–wellhofer). All the data were normalized to be unity at a depth of 10 cm. (b) Comparison between the measured and the calculated dose profile at a depth of 10 cm for a 40 × 40 cm2 field with 6 MV x-rays. A diode detector (PFD, Scanditronix–wellhofer) was used for the measurements.

Image of FIG. 4.
FIG. 4.

Comparison between the relative depth dose at the clinical dose rate (RDD1) and that at the extremely low dose rate (RDD2).

Image of FIG. 5.
FIG. 5.

The changes of the photon energy distributions (a) for the different field sizes, (b) for the different depths, and (c) for the various distances from the field edge (referred to as X edge) for a 10 × 10 cm2 field, calculated with GEANT4. The three geometries are the same as those in the TEPC measurements. The total amount of fluence in each distribution is normalized to be unity. The size of energy bins is 0.1 MeV. The error bars represent the statistical uncertainty (1 SD).

Image of FIG. 6.
FIG. 6.

Field size dependence of the measured values (left vertical axis) and the calculated RBEMK for cell killing of the HSG tumor cells at the 10% survival level (right vertical axis). The error bars represent 1 SD of . An overall uncertainty of approximately 6% for the RBEMK values, which is including both the error of the value and the error for the reproduction of the experimental RBE, is not shown in the figure.

Image of FIG. 7.
FIG. 7.

Depth dependence of the measured values (left vertical axis) and the calculated RBEMK for cell killing of the HSG tumor cells at the 10% survival level (right vertical axis). The error bars represent 1SD of . An overall uncertainty of approximately 6% for the RBEMK values, which is including both the error of the value and the error for the reproduction of the experimental RBE, is not shown in the figure.

Image of FIG. 8.
FIG. 8.

The measured values (left vertical axis) and the calculated RBEMK for cell killing of the HSG tumor cells at the 10% survival level (right vertical axis) perpendicular to the central beam axis for the different field sizes. The error bars (1SD) of only for a 1 × 1 cm2 field are typically shown in the figure, because those for the other field sizes are almost the same. An overall uncertainty of approximately 6% for the RBEMK values, which is including both the error of the value and the error for the reproduction of the experimental RBE, is not shown in the figure.

Image of FIG. 9.
FIG. 9.

Microdosimetric distributions y-yd(y) at the different positions perpendicular to the central beam axis for a 15 × 15 cm2 field. The open and the closed symbols represent the distributions inside and outside the field, respectively.

Image of FIG. 10.
FIG. 10.

The percentage of the photon fluence below 200 keV calculated with GEANT4 for the various field sizes. The total amount of fluence in each distribution is normalized to be unity. The error bars represent the statistical uncertainty (1 SD).

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/content/aapm/journal/medphys/38/8/10.1118/1.3613152
2011-07-28
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Microdosimetric study on influence of low energy photons on relative biological effectiveness under therapeutic conditions using 6 MV linac
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/38/8/10.1118/1.3613152
10.1118/1.3613152
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